Field of Invention
The present invention relates generally to a power over Ethernet system, and more particularly to an inspection device and method for dynamically adjusting supplied powers to powered devices in a power over Ethernet system.
Related Art
Power over Ethernet (PoE) has found widespread application in many areas. For example, IEEE has released two standards that relate to PoE-IEEE 802.3af in 2003 and IEEE 802.3at in 2009. These standards are adopted by many applications. In this disclosure, these relevant standards relevant to the PoE will be referred to as the “PoE standard” hereinafter. PoE technology allows supplying electric power through Ethernet to devices such as Internet phone, wireless stations, network cameras, hubs, and even computers without the need of extra power outlet. Combining data transmission and power supply, PoE technology can reduce the cost and complexity of the overall network computing system.
In a power over Ethernet (PoE) system, the electric power is provided by the power source equipment (PSE) via Ethernet data cable to the powered device (PD). The power source equipment may include an Ethernet switch, a router, or other network switching and midspan devices. In the PoE system, a powered device is connected to the network and configured to obtain or request power from the power source equipment over the network.
In a PoE system, the power source equipment may connect to multiple powered devices through their network connecting ports, but may also connect to devices that will not or cannot obtain power from the power source equipment. In a real application, the powered device may include devices that are in compliance with the PoE Standard, and devices that are compatible with the PoE Standard. The PoE Standard provides that, before a power source equipment may provide power to a powered device, the power source equipment must determine whether the particular powered device is in compliance with the PoE standard. In addition, most of the power source equipment, or the power supply equipment that incorporates power source equipment, will also determine whether a device is compatible with the PoE standard. This may include a legacy device that is compatible with the PoE Standard. If compatible, the power source equipment will also provide power to such compatible device.
Under the PoE standard, when carrying out said inspection, the power source equipment provides a signal to the connecting port of a target device, and detects the response signal from the connecting port. If the response signal indicates a signature resistance ranging from 19 k to 26.5 k ohms, then the device is determined to be a powered device in compliance with the PoE standard, i.e., a qualified powered device. The PoE Standard also specifies that the voltage provided by the power source equipment should be between about 2.8 V and 10 V, the current should be less than about 5 mA, and the voltage difference of the testing signal should be more than 1 V.
During the inspection, a typical method is for the power source equipment to apply a voltage or current to the particular connecting port, and then to measure the response signal from the target device after a predetermined period. The signature resistance is calculated based on the current/voltage relationship from the two signals. If a current is applied, the current is normally in the range of 150 μA to 400 μA, and the voltage of the connecting port is measured to calculate the value of the signature resistance. In this case, a target device in compliance with the PoE standard will cause the power sourcing device to detect an about 2.8 V to 10 V voltage drop in the connecting port.
Alternatively, if the testing signal is a voltage signal, the voltage is generally between about 2.8V to 10V, and the detected current value shall be between about 87.5 uA to 625 uA.
Based on the result, the power source equipment will decide whether to perform classification on the powered device. From the classification, the power source equipment may provide different power levels to different powered devices.
To classify the powered device, the IEEE 802.3 of/at standard provides five classes (classes 0, 1, 2, 3, and 4) with respective power allocation upper limits (15.5 W, 4 W, 7 W, 15.5 W and 30 W). In reality, many powered devices with low power consumption will also label themselves as high power-allocated device. For example, a powered device with a normal power range of 7 W may label itself as class 4. This is to prevent the operation of the powered device being discontinued due to power supply limit from the power source equipment of the PoE system. This, however, will also cause the power source equipment to reserve 30 W for the powered device. Since the powered device only uses 7 W, the remaining reserved power will not be able to be allocated to other powered devices connected to the connecting port, thereby causing power allocation waste.
Specifically, when a power source equipment is to supply power to a newly-added powered device, it will sum the allocated power values of all connected powered devices that it currently supplies power to. It will then compare the summed value with the total power supply value that the PoE system is capable of supplying. The difference of the two is then to be compared with the newly-added powered device based on its classification. If the power allocation requested is greater than the difference, then no power will be supplied to the newly-added powered device, or the power supplied to a connected powered device with lower priority will be stopped. Once stopped, the sum of the difference and the power allocation values of the stopped device, or part of the sum thereof, will be allocated to the newly-added powered device. In some cases, the newly-added powered device may only need 7 W but still labels itself with high power level. This will cause the PoE system not being able to supply power to the newly-added powered device, or may cause the PoE system stop supplying power to another with lower priority.
Under this situation, a known technique is to calculate two parameters in addition to the total power supply the PoE system is capable of supplying, and the maximum power from the powered devices that the PoE system is currently supplying power to or waiting for the power supply. The two parameters include the maximum total power consumption and the critical power value. In a PoE system, the total power supply>maximum total power consumption>critical total power value. In addition, this method will also specify priority for each connected powered device. The PoE system will continue monitoring the total power consumption from the powered devices it supplies. When the total power consumption surpasses the maximum total power consumption, it will stop supplying power to powered devices with lower priority. When the total power consumption is lower than the critical total power value, the PoE system will supply power to additional, connected powered devices based on their priority levels. When the total power consumption is between the maximum total power consumption and the critical total power value, the PoE system will stop supplying power to a powered device with lower priority to provide power allocated to the low priority device to powered devices with higher priority. Details of the above-mentioned technique can be referred to in U.S. Pat. No. 7,257,724, entitled “Method and Apparatus for Power Management in a Local Area Network.” One drawback of such technique is that the powered devices with low priority may often suffer power outage, and sometimes may not even obtain any power from the PoE system.
Another known technique is for the PoE system to measure the real power consumption of the powered devices. For example, in case where a powered device with only 7 W power consumption is labeled with class 4 specification, the system will lower the classification of the powered device to a lower one. For example, it may classify the powered device with just the classification that has an upper power limit that is just above the real power consumption. This method will indeed increase the power allocation efficiency at that time, but can still cause powered devices to suffer power outage even when there is available power to supply.
For example, a common powered device is an IP cam. The power consumption of the powered device may be as illustrated in FIG. 3. As shown, when the system starts supplying power to the powered device, the powered device and the computer (server) will be engaging in connection setting at time T1, and will not need a full power to operate. At this moment, if the PoE system measures the actual power consumption of the powered device, it will mistakenly reduce its power classification. Now, when the IP cam wants to begin initiating a full data transmission or night lighting at time T2, the power consumption needs to be dramatically increased, as illustrated in the dash line in FIG. 3. Because the powered device now has a lowered classification, at time T2, the powered device may shut down due to power overload. Furthermore, when the PoE system re-supplies power to the IP cam the next time, the whole situation will repeat to cause the powered device to shut down again and again.
Yet there is no power source equipment of the PoE system that can overcome the inefficient power allocation due to the difference between the classification power allocation and the real power consumption. In addition, currently there is no power source equipment of the PoE system that is able to render the power difference between its classification setting and its real power consumption to other powered devices, especially the powered devices with lower priorities.